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FreeBSD-SA-20:25.sctp                                       Security Advisory
                                                          The FreeBSD Project

Topic:          SCTP socket use-after-free bug

Category:       core
Module:         kernel
Announced:      2020-09-02
Credits:        Megan2013678@protonmail.com
Affects:        All supported versions of FreeBSD.
Corrected:      2020-08-24 09:19:05 UTC (stable/12, 12.1-STABLE)
                2020-09-02 16:24:32 UTC (releng/12.1, 12.1-RELEASE-p9)
                2020-08-24 09:46:36 UTC (stable/11, 11.4-STABLE)
                2020-09-02 16:24:32 UTC (releng/11.4, 11.4-RELEASE-p3)
                2020-09-02 16:24:32 UTC (releng/11.3, 11.3-RELEASE-p13)
CVE Name:       CVE-2020-7463

For general information regarding FreeBSD Security Advisories,
including descriptions of the fields above, security branches, and the
following sections, please visit <URL:https://security.FreeBSD.org/>.

I.   Background

The Stream Control Transmission Protocol (SCTP) is a message oriented
transport protocol supporting arbitrary large user messages.
It can be accessed from applications by using the the socket API.

II.  Problem Description

Due to improper handling in the kernel, a use-after-free bug can be triggered
by sending large user messages from multiple threads on the same socket.

III. Impact

Triggering the use-after-free situation may result in unintended kernel
behaviour including a kernel panic.

IV.  Workaround

No workaround is available.

V.   Solution

Upgrade your vulnerable system to a supported FreeBSD stable or
release / security branch (releng) dated after the correction date,
and reboot.

Perform one of the following:

1) To update your vulnerable system via a binary patch:

Systems running a RELEASE version of FreeBSD on the i386 or amd64
platforms can be updated via the freebsd-update(8) utility:

# freebsd-update fetch
# freebsd-update install
# shutdown -r +10min "Rebooting for a security update"

2) To update your vulnerable system via a source code patch:

The following patches have been verified to apply to the applicable
FreeBSD release branches.

a) Download the relevant patch from the location below, and verify the
detached PGP signature using your PGP utility.

[FreeBSD 12.1]
# fetch https://security.FreeBSD.org/patches/SA-20:25/sctp.12.1.patch
# fetch https://security.FreeBSD.org/patches/SA-20:25/sctp.12.1.patch.asc
# gpg --verify sctp.12.1.patch.asc

[FreeBSD 11.4]
# fetch https://security.FreeBSD.org/patches/SA-20:25/sctp.11.4.patch
# fetch https://security.FreeBSD.org/patches/SA-20:25/sctp.11.4.patch.asc
# gpg --verify sctp.11.4.patch.asc

[FreeBSD 11.3]
# fetch https://security.FreeBSD.org/patches/SA-20:25/sctp.11.3.patch
# fetch https://security.FreeBSD.org/patches/SA-20:25/sctp.11.3.patch.asc
# gpg --verify sctp.11.3.patch.asc

b) Apply the patch.  Execute the following commands as root:

# cd /usr/src
# patch < /path/to/patch

c) Recompile your kernel as described in
<URL:https://www.FreeBSD.org/handbook/kernelconfig.html> and reboot the
system.

VI.  Correction details

The following list contains the correction revision numbers for each
affected branch.

Branch/path                                                      Revision
- -------------------------------------------------------------------------
stable/12/                                                        r364644
releng/12.1/                                                      r365256
stable/11/                                                        r364651
releng/11.4/                                                      r365256
releng/11.3/                                                      r365256
- -------------------------------------------------------------------------

To see which files were modified by a particular revision, run the
following command, replacing NNNNNN with the revision number, on a
machine with Subversion installed:

# svn diff -cNNNNNN --summarize svn://svn.freebsd.org/base

Or visit the following URL, replacing NNNNNN with the revision number:

<URL:https://svnweb.freebsd.org/base?view=revision&revision=NNNNNN>

VII. References

<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-7463>

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-SA-20:25.sctp.asc>
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